PC Peripherals Gigabyte 8x mobo fan speed control query ...

[PoBoy]

Fan speed control is not really discussed much here, but I'm hoping @cranky will respond.

I'm finally upgrading to Haswell and came across this :

The board has a pair of 4-pin PWM fan headers but this is deceiving as the SYS_FAN header can only be controlled via voltage.

here: http://www.silentpcreview.com/article1363-page6.html

Does that mean that using headers like the SYS_FAN above :
1) Either 4-pin (PWM) fans or 3-pin fans can be used.
2) Fan speed is controlled for 4-pin PWM fans or 3-pin fans using (only) voltage ( i.e PWM if present on the fan is ignored, i.e. there is no advantage in using a PWM fan).

 

[cranky]

1. Yes.

2. No. Only 4 pin fans will enjoy speed control. If the controller does not sense the pwm feedback pin, it cannot provide pwm control. It has no intelligence to switch to a linear control mode.

As of this moment I am running a gigabyte mono with a 3 pin fan connected to the sys fan header and it runs at full speed unless I use a zener in series to drop it down to 5v. The sensor is also not able to accurately read the fan speed, let alone control it.

I suspect that it will be something that changes regularly with manufacturers constantly trying to address feedback. This has to be worked out on a case to case basis.

 

[PoBoy]

Thanks.
But, getting a bit confused. For the board mentioned in the OP, since "the SYS_FAN header can only be controlled via voltage" I thought it meant the voltage supplied to the fan can be controlled/changed. If the voltage is reduced, won't the fan speed also reduce ? Even for a 3-pin fan.

 

[cranky]

Yes to your question, but no to the generalisation.

Pwm fans do not respond to voltage control very well. And 3pin fans do not have any clue about pwm. Which means that the fan control or lack thereof will differ on a case to case basis.

The reason I highly doubt that a 4pin connector will offer voltage control is that any fan connected to it correctly will not operate correctly and hence, there is no point of using a 4pin connector. Also, both the b75 boards I have offer fine grained slope control in the BIOS for both headers, which is not possible on a voltage control header. One is a gigabyte board, so I wouldn't know why they would degrade it. One way to work it out is connect your CPU fan to that header and see if it is able control speed correctly.

Now to voltage and fan speed. Pwm fans should be operated only at their rated voltage, as they will make terrible noises when operated below or above it. Yes, voltage will reduce the speed, but that is not the objective, noise reduction is, and that is best achieved using pwm for a pwm (4 pin) and voltage control for a 3pin fan.

Does that clarify?